The invention relates to fuel injection systems for internal combustion engines. More particularly, the invention relates to mechanical fuel pumps, injectors, and control systems for small internal combustion engines.
It is a goal in the design of internal combustion engines to reduce emissions that may be harmful to the environment. Attempts to achieve this goal have included calibrating the fuel nozzle in a small engine carburetor to deliver just enough fuel as is necessary to run the engine at wide open throttle (WOT), thereby creating a controlled air-to-fuel ratio. Typically, the fuel nozzle delivers amounts of fuel into the carburetor from a fuel source in proportion to the speed of the air flowing through the carburetor throat.
The use of carburetors in small internal combustion engines tends to result in fuel flow rates that are different for various production engines. Another way of reducing harmful emissions is to precisely control the fuel metering from one engine to the next.
Small engines typically include speed governors that position the throttle valve in response to changes in speed of the engine. When the engine is running steadily at full speed, the governor is satisfied with the throttle lever position. When the engine speed decreases due to a sudden increase in load, the volume of air drawn through the carburetor may be reduced before the governor can respond. When the speed governor finally does respond, it may over-shoot the desired throttle setting. Consequently, the amount of fuel drawn through the fuel nozzle is inadequate and the air-to-fuel ratio drops below that which is necessary to support the increased load. For small engines experiencing an increased load, such engine slow-down or speed droop may cause the engine to stumble and stall for want of the correct mixture of air and fuel.
The problem is solved in larger engines (e.g., automobile engines) by incorporating an electronic fuel injection system that is controlled by an electronic control module. Such electronic fuel injection systems are typically expensive and often inappropriate for small engine applications because of the cost sensitivity of the small engine market.
The present invention provides a mechanical variable pump, fuel injector, and controller for a spark-ignited internal combustion engine. The variable pump includes at least two displaceable members at least partially defining a pump chamber. One displaceable member is movable in response to an actuating force. The volume of the pump chamber decreases and increases cyclically in response to movement of the displaceable members, thereby increasing and decreasing, respectively, the pressure within the pump chamber.
The second displaceable member is moved by a spring and the pressure differential between atmospheric pressure and the pressure in the pump chamber. The movement of this displaceable member is limited by two stop members. One stop member is fixed and the other stop member is adjustable. The position of the adjustable stop member determines the amount of fuel that is pumped in a given cycle.
The adjustable stop member is preferably movable in response to the speed- and throttle-related movement of an engine component. Movement of the second displaceable member is limited as a function of the position of the adjustable stop member. The increase and decrease in pump chamber pressure are therefore dependent at least partially on the position of the adjustable stop member.
Preferably, the two displaceable members are flexible members or diaphragms. Preferably the actuating force is provided by one of a movable engine member (e.g., a cam shaft, cam gear, rotating eccentric bearing, piston, or flywheel), and pressure pulses within the engine.
A biasing member, such as a return spring, may bias the movable member against a cam of the rotating member. The movable member cyclically applies an actuating force to the first displaceable member to move the first displaceable member from a rest position in a positive direction in response to cam rotation or the movement of another engine component. The return spring biases the movable member in a negative direction, opposite the positive direction, to the rest position for each rotation of the cam or movement of another engine component. Alternatively, the movable member may be biased by another rotating engine component other than a cam. It could also be biased by an eccentric bearing on a shaft.
Preferably the adjustable stop member engages the second flexible member to limit its deflection in the negative direction. Preferably, the variable pump includes a second stop member that limits deflection of the second flexible member in the positive direction. A return spring may be used to bias the second flexible member toward the positive direction.
Preferably, the pump chamber is substantially airtight except for an inlet valve and an outlet passage to the fuel injector. The inlet valve is a one-way valve that only allows fluid flow into the pump chamber from a fuel source. The outlet passage allows fluid flow from the pump chamber to the fuel injector.
The fuel is injected into a mixing chamber in the air intake passageway, an air intake manifold, or other chamber through which air is introduced into the combustion chamber during the intake stroke. The inlet valve and fuel injector are each characterized by a xe2x80x9ccracking pressure,xe2x80x9d at which the valve or fuel injector opens.
The second flexible member also deflects, in response to the cyclical deflection of the first flexible member, to the extent permitted by the adjustable stop member and the optional second stop member. Continued deflection of the first flexible member after the second flexible member is stopped results in a decrease or increase in the pump chamber volume and a resulting increase or decrease in pressure in the pump chamber. When the pressure in the pump chamber drops to the cracking pressure of the inlet valve, fuel is draw into the pump chamber. When the pressure reaches the cracking pressure of the fuel injector, fuel is expelled from the pump chamber and through the fuel injector.
The fuel injector includes a fuel nozzle in fluid flow communication between the pump and the mixing chamber. The fuel nozzle is biased with a return spring or other biasing member toward a closed position so that fuel is not allowed to flow into the mixing chamber except when the pressure is high enough. Preferably, the fuel expelled from the pump chamber provides enough pressure to open the fuel nozzle so that fuel is admitted into the mixing chamber. Preferably, the fuel injector includes a flexible member, such as a diaphragm, that deflects in response to fuel pressure to permit fuel to spray into the mixing chamber.
The change in pump chamber volume is dependent on the positions of the stop members. Therefore, the amount of fuel drawn into and expelled from the pump chamber is also dependent on the positions of the stop members. Preferably, the amount of deflection permitted by the second stop member is fixed. Preferably, the engine includes an automatic mechanical control system, such as a speed governor, that senses the speed of the engine and throttle position, and adjusts the position of the adjustable stop member accordingly. When the engine is running at a normal operating speed and load, the control system may position the adjustable stop member so that just enough fuel is pumped to keep the engine running. When the engine speed droops due to an increased load, the control system may position the adjustable stop member so that increased amounts of fuel are pumped and the engine does not stumble and/or stall.